In several technical fields, illumination is either the main purpose or is used as a tool for obtaining desired results. Applications comprise, e.g., image and movie projection, photolithography, computer-to-plate applications, serigraphy, other photographical applications such as production of printed circuit boards, etc., photolysis, rapid prototyping, rapid manufacturing, communication, and several others.
Numerous categories and types of light sources exist for illumination purposes, each manufactured with different purposes in view and often constrained to neglect other purposes. Purposes of interest may be power rating, luminous efficacy, stability of the luminous intensity, precision of the point of emission, color rendering, etc. For example, short arc lamps, i.e., high-pressure discharge lamps, are used in many applications because they may offer high power ratings, high luminous efficacy, excellent color rendering and a very small point of emission. Unfortunately, their construction, however, also causes displacement of material from the electrodes, causing their voltage ratings to change during use, their lifetime to be reduced, and the point of emission, i.e., the arc, to fluctuate. These problems are well known within the art and are addressed in several ways, some of which include the use of alternating driving current and/or frequent current peaking. Often such solutions introduce new problems and in the example of short arc lamps, the current peaking causes the emitted luminous intensity to fluctuate.
Of the above mentioned illumination applications, several do accept light sources establishing light beams having fluctuating luminous intensity and/or fluctuating point of emission, either because they are intended for use in low-quality products, or because the fluctuations may be considered insignificant for a specific use. For example, for use in movie projectors, a slightly fluctuating luminous intensity may be acceptable as the light beam is used to illuminate the same area continuously, for which reason the human eye may not be able to recognize the changes and, furthermore, the projected images are changed at a fast pace. Such fluctuations may, however, not be acceptable for specific uses of a high quality projector.
In fields as, e.g., photolithography and other techniques where the region to be exposed is only illuminated little by little, fluctuations of the luminous intensity may, however, be considered hazardous. This is because different regions of the exposed medium, e.g., a printing plate, are illuminated in turn, which makes it possible for one region to be illuminated with one level of intensity and the adjacent region to be illuminated with another. This may cause the result to look inconsistent and the probable periodicity of the intensity changes may even cause stripes or other visible periodical patterns to occur.
One of several objects of the present invention is to establish compensation means for facilitating the use of light sources with varying luminous intensity, e.g., short arc lamps with additional intensity at the supply peaking times, in applications where typically only constant intensity lamps are used.
One of several objects of the present invention is to establish means that adapt to real-time changes in the level of periodically occurring additional luminous intensity in a light beam and thus facilitate compensation in order to utilize such a light beam in applications where typically only constant intensity light beams are used.
One of several objects of the present invention is to facilitate an improved uniform light transmission via a spatial light modulator, such as, e.g., a DMD-modulator.